Fix up documentation

model/group.go

@@ -88,13 +88,15 @@ func (g *Group) CheckGroup() bool {
 	return g.GroupID == deriveGroupID(g.GroupKey[:], g.GroupServer)
 }
 
+// deriveGroupID hashes together the key and the hostname to create a bound identifier that can later
+// be referenced and checked by profiles when they receive invites and messages.
 func deriveGroupID(groupKey []byte, serverHostname string) string {
 	data, _ := base32.StdEncoding.DecodeString(strings.ToUpper(serverHostname))
 	pubkey := data[0:ed25519.PublicKeySize]
 	return hex.EncodeToString(pbkdf2.Key(groupKey, pubkey, 4096, 16, sha512.New))
 }
 
-// Compromised should be called if we detect a a groupkey leak
+// Compromised should be called if we detect a groupkey leak
 func (g *Group) Compromised() {
 	g.IsCompromised = true
 }